Metal Bellows and Movements of Metal Expansion Joints

What is a Metal Bellow?

Metal bellows are the essential component of expansion joints and compensators. They are produced by forming a cylinder first from thin rolled sheets of metals by specialized welding process for welding the seam and then forming circumferential convolutions on these cylinders as shown. Rarely seamless cylinders are used for smaller size bellows. Metal bellows only as intermediate components for the manufacture of expansion joints and compensators can be supplied if the purchaser has the technology to weld the end fittings to the thin walled bellows elements.

Formation of Metal Bellows from plain Cylinder

Different movements of Metal Bellows

How does a Metal Bellow work?

The metal bellows are designed to contain the operating pressure of the pipeline while absorbing the movements and vibrations in the pipeline at the operating temperature. The metal bellows can basically absorb three types of movements or a combination of all the three as shown. Angular movement is the least severe of the three types and lateral movement is the most severe movement on the bellows. Although metal bellows can absorb torsional movement to a very small extent they are not designed for torsional movement and should be avoided by all means.